What is the risk of miscarriage associated with a subchorionic hematoma in early pregnancy?

Risk of Miscarriage with Subchorionic Bleeding

Subchorionic hematoma in early pregnancy increases the risk of miscarriage to approximately 17–34%, compared to 6.5–12.6% in pregnancies without hematoma. 1, 2, 3, 4

Baseline Risk Assessment

The overall miscarriage risk varies based on the presence and characteristics of the hematoma:

• Without subchorionic hematoma: Baseline miscarriage risk is 6.5–12.6% in early pregnancy 2, 4
• With subchorionic hematoma: Miscarriage risk increases to 17–34% 1, 2, 3, 4
• First trimester bleeding overall: Occurs in 7–27% of all pregnancies, with an overall miscarriage risk of approximately 12% 5

Critical Prognostic Factors

Hematoma Size

Large hematomas carry significantly higher risk than small or medium-sized hematomas:

• Small hematomas: Similar miscarriage rates to controls 1
• Medium-sized hematomas: Significantly increased risk of placental abruption and early pregnancy loss compared to controls 1
• Large hematomas: Markedly elevated risk with early pregnancy loss rates significantly higher than both smaller hematomas and controls (p < 0.001) 1

However, one study found no correlation between hematoma size and pregnancy loss 3, and another reported that size did not affect outcome 2, suggesting size may be less predictive than other factors.

Hematoma Location

Location is a more critical determinant than volume:

• Corpus or fundal location: Most hematomas associated with abortion were found in the corpus or fundus of the uterus (p = 0.03) 2
• Supracervical location: Better prognosis than corpus/fundal placement 2
• Retroplacental hematomas: Significantly higher miscarriage rate than subchorionic hematomas 6

Presence of Fetal Cardiac Activity

The single most important favorable prognostic factor is documented fetal cardiac activity:

• Prognosis is significantly better when fetal cardiac activity is present at the time of hematoma diagnosis 5, 7
• This should be documented using M-mode ultrasound or video clips, avoiding pulsed Doppler in the first trimester due to potential bioeffects on the developing embryo 5, 7, 8

Risk Stratification Algorithm

Use this framework to counsel patients:

1. Highest risk (>30% miscarriage): Large hematoma + corpus/fundal location + no fetal cardiac activity 1, 2

2. Moderate-high risk (20–30% miscarriage): Medium-to-large hematoma OR retroplacental location, with fetal cardiac activity present 1, 3, 6

3. Moderate risk (15–20% miscarriage): Small-to-medium subchorionic hematoma in supracervical location with fetal cardiac activity 2, 4

4. Lower risk (approaching baseline): Small subchorionic hematoma with fetal cardiac activity and favorable location 1, 2

Additional Adverse Outcomes Beyond Miscarriage

For pregnancies that continue beyond the first trimester, subchorionic hematoma is associated with:

• Preterm delivery (<37 weeks): Significantly increased, especially with large hematomas (p < 0.001) 1, 6
• Placental abruption: Increased risk with medium and large hematomas (p = 0.002) 1, 6
• Intrauterine growth restriction (IUGR): Significantly higher with large hematomas (p = 0.003) 1, 6
• Lower gestational age at delivery: Regardless of hematoma size (p < 0.001) 1
• Cesarean section: Increased rate (60% vs controls, p < 0.001) 6
• Low birth weight and lower Apgar scores: More common in hematoma group 6

Clinical Management Implications

Serial ultrasound monitoring is recommended:

• Follow-up ultrasound examinations at 7-day intervals until bleeding ceases, hematoma disappears, or pregnancy outcome is determined 7
• Document hematoma location relative to the placenta, size as percentage of gestational sac, and presence of fetal cardiac activity 5, 7
• All subchorionic hematomas typically disappear by the second trimester, but 2% of retroplacental hematomas may persist 6

Common Pitfalls

• Do not rely solely on hematoma size: Location and presence of fetal cardiac activity are equally or more important prognostic factors 2
• Do not perform digital pelvic examination: Until ultrasound excludes placenta previa, low-lying placenta, and vasa previa 7, 8
• Do not use pulsed Doppler in first trimester: Use M-mode ultrasound to document cardiac activity instead 5, 7, 8
• Do not forget Rh status: Administer 50 μg anti-D immunoglobulin to Rh-negative patients with any first trimester bleeding 5, 7